1. Field of the Invention
The present invention relates to a method and apparatus for measuring the characteristics of an insulated film (inner charge amount, film thickness, relative dielectric constant, etc.) formed on a semiconductor substrate.
2. Description of Related Art
In the semiconductor device production process, various films including an insulator film are formed on a semiconductor substrate. The characteristics of the insulator film have a great influence on the characteristics of the semiconductor device. It is therefore inevitable to evaluate the characteristics of the insulator film during the semiconductor device production process.
With the progress of semiconductor device integration technology, the type and thickness of an insulator film to be used have undergone a change. This has consequently changed the insulator film evaluation method. For example, there have been instances where an optical method (e.g., ellipsometry) is used as a method of measuring the thickness of an insulator film. Such an optical measuring method may not always be accurate under the influence of an organic substance attached to the insulator film surface. Therefore, attention is now placed on an electric film thickness measuring method directly related to the device operation.
With the change in the type of an insulator film, the relative dielectric constant of the insulator film becomes an important parameter. It is therefore required to measure more accurately the relative dielectric constant of the insulator film.
The insulator film thickness can be obtained when the surface charge amount, the surface voltage and the relative dielectric constant are known. The relative dielectric constant of an insulator film can be obtained when the surface charge amount, the surface voltage and the film thickness are known. Accordingly, when either the film thickness or the relative dielectric constant is known in addition to the surface charge amount and the surface voltage, the other can be obtained.
In order to stably form a high-quality insulator film, it is important to control the inner charge amount of an insulator film. It is therefore required to measure more accurately the inner charge amount of the insulator film.
There is a method of measuring the film thickness, relative dielectric constant, or inner charge amount of an insulator film, in which electrodes are formed on the surface of the insulator film. However, this method is not a preferable measuring method, because this is a destructive test and includes a number of processing steps. There can be also considered using mercury as electrodes. However, the mercury is detrimental to the human body and is therefore troublesome to deal with. Besides, since mercury is a liquid, which does not stabilize its electrode area, so that an accurate measurement cannot be achieved. Furthermore, in either event, when the electrodes are formed on the surface of the insulator film, this involves the likelihood that an electric current leaks through the insulator film at the time of measurement, making the measurement inaccurate.
It is therefore desired to establish a method of measuring, in a non-contact manner, the insulator film characteristics such as the thickness, relative dielectric constant, or inner charge amount of an insulator film. Such a measuring method proposes a technique of measuring the surface charge amount and surface voltage of an insulator film at the time when the surface of the insulator film is charged, and of obtaining the thickness or relative dielectric constant of the insulator film based on the values thus measured (United States Patent Application Publication No. US2004/0019442A1). However, the measurement of other physical quantities such as inner charge amount, surface voltage change due to a surface adsorbed substance, or substrate carrier concentration has not been proposed.
Another earlier technique of measuring the thickness of an insulator film is disclosed in U.S. Pat. No. 5,485,091. However, with this earlier technique, the relative dielectric constant, inner charge amount, surface voltage change due to a surface adsorbed substance, or substrate carrier concentration of an insulator film cannot be obtained.
In recent years, with the progress of semiconductor device integration technology, there has been a new problem of adsorption of an organic substance on the insulator film surface. More specifically, in a clean room, there exists a large amount of organic substances detached from resins or the like. These organic substances are adsorbed on the insulator film surface, thereby causing a problem at various processing steps. Therefore, it is important to control such that no organic substance generates in the substrate processing apparatus. In order to achieve this, it is required to measure the adsorption of an organic substance on the substrate surface. The amount of the organic substance in an atmosphere or on an insulator film can be measured by chemical analysis. However, the measurement by chemical analysis is time consuming. Accordingly, when the chemical analysis is applied, particularly to the measurement of the organic substance attached to the surface of an insulator film on a substrate, organic substance contamination associated with in-line cannot be measured.
Therefore, a need exists for a convenient measuring technique capable of electrically measuring the adsorption of an organic substance on an insulator film.
The insulator film surface voltage can be measured with a Kelvin probe. However, in light of the influence by the inner charge amount or surface charge amount of an insulator film, the measurement of the surface voltage change due to a surface adsorbed substance attached to the insulator film surface has not been performed.